Electron transfer kinetics of self-assembled ferrocene (C12)Alkanethiol monolayers on gold electrodes from 125 K to 175 K

Abstract

The electron transfer kinetics of monolayers of CpFeCpCO2(CH2)12SH and CH3(CH2)11SH co-chemisorbed on gold electrodes have been measured in 2: 1 (v: v) chloroethane/butyronitrile solvent at temperatures ranging from 125 K to 175 K with potential steps and cyclic voltammetry. Rate constants, ko, measured using cyclic voltammetry range from 3 × 10−4 to 10−1s−1 over these temperatures; an activation plot of log[ko/kb T1/2] vs. 1/T gave λ = 0.89eV for the reorganization energy for the Cp2Fe+/0 reaction and a pre-factor of 6.5 × 106eV−1 + s− 1. The rate constants were obtained by comparison of experimental ΔEPEAK values with those of cyclic voltammograms digitally simulated with Marcus-DOS theory. A value of λ = 0.76eV is predicted from dielectric continuum theory. The CpFeCpCO2(CH2)12SH monolayers are kinetically inhomogeneous (disperse) as shown by non-linear In[i] vs. time plots in potential step experiments. The kinetic dispersity has adverse effects on determinations of λ values from cyclic voltammetric waveshapes and from plots of potential step-derived rate constants, kapp,η′, against overpotential (η), producing depressed values for λ.